The present invention relates to chair bases, particularly height adjustable chair bases. The most common type of height adjustable chair bases comprises a threaded post extending downwardly from the chair seat being threaded in a nut which in turn is rotatably carried on top of a hub tube. To adjust the height of the chair, one grasps the nut assembly with one hand and rotates the chair with the other.
One problem with such a chair base is that the threaded spindle is rather unsightly in appearance when the chair is adjusted in one of its higher positions. Also, the spindle has to be very large in diameter in order to be sufficiently strong to take the lateral loads which are imposed upon it when a person sits in the chair, particularly when a person leans back in the chair. The threaded spindle must also be greased and hence is sometimes the source of contamination of carpeting or a person's clothing. It is also somewhat cumbersome to adjust the height of the chair in that one has to reach under the chair, grasp the nut and then try to rotate the chair without getting hit in the chin.
Some chain braces, such as that disclosed in U.S. Pat. No. 3,799,485 to Wolters seek to eliminate the exposed threaded spindle by providing a column extending downwardly from the chair seat and being telescopically received within the hub tube. The column includes a nut located in the bottom thereof which is threaded on a threaded post extending upwardly within the hub tube. Normally, the threaded post and the nut rotate together as a person rotates his chair. However by reaching under the chair base and pushing upwardly on a button, one can lock the threaded post against rotation. Then one can rotate the chair and the nut will thread upwardly or downwardly on the threaded post. This type of mechanism is generally complicated and is not particularly economical to assemble. Further, it is generally considered somewhat cumbersome to use this mechanism in that one still has to reach clear under the chair base, depress the button and then rotate the chair, again trying to avoid getting hit in the chin by the rotating chair.
Others have developed devices which include some form of spring biased detent means which allow you to adjust the height of the chair by simply rotating the unoccupied chair. One does not have to reach under the chair and grasp any part of the base or push any buttons. Yet when one sits in the chair, the detent means is disengaged from either the threaded spindle or nut such that upon rotation of the chair, the height of the chair does not change. Two examples of many such devices include Richards U.S. Pat. No. 2,792,975 and Bouman U.S. Pat. No. 2,026,298.
Typically, these mechanisms involve the use of a threaded spindle extending downwardly from the chair seat, and therefore have the unsightliness, grease and strength problems cited above. Sometimes cover tubes are employed to try to hide the threaded spindle. However such mechanisms have typically been very complicated and difficult to assemble. Alternatively, it is difficult to design them without creating strength problems.
Thus, there has long been a need for a height adjustable chair base which can be adjusted by rotating the seat when it is unoccupied without having to reach under the seat and grasp some portion of the chair base, which can be easily and economically assembled, which does not incorporate inherent strength limitations and which avoids the employment of a threaded post extending downwardly from the chair seat.